The present invention relates generally to an electroplating apparatus. More specifically, the present invention relates to an apparatus for producing finely structured, thick metal depositions on semiconductor wafers.
Humps, electroplated onto a chip component, that project above the chip surface are required for micropack technology, a format for integrated circuits. Typically, these humps project approximately 18 um above the chip surface. In plan view, the hump generally possesses a quadratic shape, whereby the lateral edges exhibit a length of approximately 140 um, 100 um and below. Despite an unfavorable starting basis that depressions of a maximum of 8 um up to the terminal pad are prescribed in the central region of the humps, the hump surface should be nearly planar.
Due to the macro-scatter capability, it is not possible with known electroplating apparatus to achieve a sufficient uniformity of hump height over the surface of the semiconductor wafer. For exaple, for a 100 mm semiconductor wafer, it is not possible with known apparatus to achieve a uniformity of 1.0 um for the hump height over the surface with the exception of a narrow edge region. Among those factors which define the scatterability, the geometrical properties of the system which determine the primary current distribution must be cited first. Included among the geometrical properties are the geometrical formulas of the anode, cathode and electrolyte vessel as well as the arrangement of the electrodes in the electrolyte vessel and their distance from the vessel walls.
The electroplating apparatus for producing finely structured, thick metal depositions on semiconductor wafers must not only achieve, to the extent possible of uniformity of hump height over the surface, but also guarantee a reproducible, uniformly good metal deposition over a period of months. Furthermore, decomposition products that hinder a good metal deposition must be prevented from collecting.
Accordingly, there is a need for an electroplating apparatus that can meet the extreme requirements needed to produce semiconductor wafers.